1. Field of the Invention
The present invention relates to a wastegate valve control device for an internal combustion engine, which is to be mounted in a vehicle (for example, a supercharged-engine vehicle), and a wastegate valve control method for an internal combustion engine.
2. Description of the Related Art
Conventionally, for the purpose of improvement of an output of an internal combustion engine (hereinafter referred to as “engine”) and the like, there is known a turbocharger including a supercharger operated by rotating a turbine with an exhaust gas, which is provided in an intake path of the engine.
In the turbocharger described above, there is a fear in that a boost pressure may increase to be higher than needed to break the engine when rotation is at high speed under high load. Therefore, an exhaust bypass passage is generally provided in parallel to the turbine. By a wastegate valve provided in the exhaust bypass passage, apart of the exhaust gas flowing through an exhaust path is diverted to pass through the bypass passage to regulate the amount of inflow of the exhaust gas into the turbine. In this manner, a pressure (boost pressure) in the intake path of the engine is controlled to an appropriate level.
Moreover, the wastegate valve is generally operated (performs an opening/closing operation) by driving an actuator (positive-pressure actuator, for example). Specifically, the wastegate valve has a mechanism to operate by the driving of the actuator when the pressure in the intake path (in particular, in a portion located upstream of a throttle valve, in which the pressure increases) of the engine becomes higher than an atmospheric pressure.
Moreover, until the driving of the actuator is enabled, the wastegate valve is normally in a fully-closed state. The wastegate valve is hereinafter referred to as “WGV”, and a wastegate valve actuator for operating the WGV is hereinafter referred to as “WGA”.
Conventionally, the WGV cannot be operated unless the pressure in the intake path of the engine becomes higher than a threshold value. Specifically, when the above-mentioned pressure is equal to or lower than the threshold value, the WGV cannot be operated. Therefore, the amount of opening of the WGV (WGV opening) cannot be changed.
Therefore, in recent years, there has been proposed a system in which the WGA is motorized to drive the WGV as needed without depending on the pressure in the intake path of the engine so that supercharging by the turbocharger can be limited. In such a system, however, there is generated an error between a detected value by a WGV opening sensor and a true WGV opening (actual WGV opening) due to the effects such as a change with time, which is caused by repeated implementation of the opening/closing operation of the WGV over a long period of time, temperature characteristics of the WGV opening sensor, or a thermal expansion of a structure constituting the WGV.
As a result, a reference position of the WGV (position of the WGV when the detected value by the WGV opening sensor becomes 0%) shifts from a full-closure position of the WGV (position of the WGV when the true WGV opening becomes 0%). Therefore, even when the WGA is operated by the same control amount, the WGV opening shifts, which sometimes prevents the WGV from being controlled to a desired open/closed state. Moreover, if a throttle upstream pressure does not reach a control target value or the position of the WGV further operates from the fully-closed state to a closing side, there is a risk in that a driving current of the WGA becomes an overcurrent. Thus, in the related art, in consideration of the effects of the shift of the reference position with respect to the full-closure position of the WGV, the amount of control of the WGA is corrected.
Specifically, during boost-pressure feedback control, a WGV-opening correction amount is calculated from a deviation between a target boost pressure and an actual boost pressure. Based on the calculated WGV-opening correction amount, the reference position of the WGV is learned (for example, see Japanese Patent No. 4434057).
Further, an estimate value of the WGV opening corresponding to an operation amount of the WGV, an estimate value of a turbo rpm calculated based on the estimate value of the WGV opening and a measured value of an intake-air flow rate, and an estimate value of a compressor flow rate calculated based on the turbo rpm and a measured value of the throttle upstream pressure are respectively calculated by using models. Then, the estimate value of the compressor flow rate and the measured value of the intake-air flow rate are compared with each other. Based on the result of comparison, the relationship between the estimate value of the WGV opening and an operation amount of the WGV is adjusted (for example, see Japanese Patent Application Laid-open Nos. 2012-225181 and 2012-241625).
However, the related art has the following problems.
In the related art described in Japanese Patent No. 4434057, a difference in the amount of change of the WGV opening for the same amount of change of the throttle upstream pressure is not taken into consideration. Therefore, in some cases, the shift of the reference position with respect to the full-closure position of the WGV cannot be accurately corrected based on the WGV-opening correction amount obtained when the WGV opening is in an intermediate range. As a result, there is a problem in that the WGV cannot be controlled to be placed in a desired open/closed state in some cases.
Further, in the related art described in Japanese Patent Application Laid-open Nos. 2012-225181 and 2012-241625, a plurality of complex models are used to obtain the estimate values of the large number of parameters. Therefore, an expensive CPU is required to deal with an increase in a processing load or in a necessary memory capacity. As a result, there is a problem in that cost is disadvantageously increased.